1. Field of the Invention
The present invention relates to a water-based ink set for ink-jet recording composed of inks of a plurality of colors.
2. Description of the Related Art
When a color image is developed by use of an ink-jet recording method, a three-color ink set has been generally used which is composed of a yellow ink (Y), a magenta ink (M) and a cyan ink (C). Moreover, a four-color ink set has also been used in which a black ink (K) is further added to the three-color ink set.
In order to develop natural colors over a wide range in a color image formed by use of the above color ink sets, hue is controlled by changing the formation ratio of dots of each of the yellow, magenta and cyan inks discharged from an ink-jet head. In addition, lightness is controlled by changing the formation density of dots of each of the inks.
Recently, in order to obtain excellent image reproducibility, a combination of inks of a plurality of colors has been employed to widen a color reproducible range. Specifically, additional inks are added to the abovementioned four-color inks (Y, M, C and K) to form an ink set composed of five to seven inks. These additional inks include a yellow ink having a low color density (a light yellow ink), a magenta ink having a low color density (a light magenta ink), and a cyan ink having a low color density (a light cyan ink). Further, Japanese Patent Application Laid-Open No. 2000-248217 proposed a method in which at least one of a blue ink (B), a violet ink (V), a red ink (R), an orange ink (O) and a green ink (G) is employed in addition to the above four-color inks (Y, M, C and K).
However, the desired chromaticity and chroma saturation are not always obtained in an ink-jet recording color image even when the light yellow, light magenta and light cyan inks are added to the conventional four-color inks (Y, M, C and K). This is also the case when the additional inks including the blue ink (B), the violet ink (V), the red ink (R), the orange ink (O) and the green ink (G) are added.
Further, in the ink set employing such additional inks, the ink ejection amount on a recording material increases relative to the number of the additional inks. Thus, if a dye is employed as the coloring agent of each ink in this ink set (hereinafter, such an ink will be referred to as a dye ink), blurring or cockling becomes noticeable on a recording material, such as ordinary paper, in which blurring is prone to occur. Also, when an ink set is composed of dye inks, environmental resistance to water, light, and gas such as ozone is unsatisfactory, and thus the storage stability of an image is insufficient.
On the other hand, in the ink set employing the additional inks in addition to the conventional four-color inks (Y, M, C and K), a pigment may be employed as the coloring agent of each ink (hereinafter, such an ink will be referred to as a pigment ink). In this case, generally, blurring is suppressed on a recording material, and also environmental resistance to water, light, and gas such as ozone is excellent. However, in many cases, the chromaticity and chroma saturation developed by use of a pigment ink are not as satisfactory as those developed by use of a dye ink. Further, when an ink set is composed of pigment inks, various problems are present such as insufficient fixability on photo glossy paper.